Recently I published an article on Starting Strength on the use of volume in strength programming for Masters. In this article, my colleague and Barbell Prescription co-Author Andy Baker and I discuss the concept of volume sensitivity in the Masters Athlete, which we have found to be just one of many programming principles for productive training in this population. We have found that Masters--adults over 40, can train more-or-less the way everybody else trains, with a few minor differences, especially as they approach intermediate status. Intermediate Masters often stagnate at high volume, and we can kick-start their progress with careful decreases in the reps, sets, or frequency, while maintaining or even increasing the load on the bar (hence, intensity-dependence).
This goes directly against your doctor's likely advice to "lift light weight for lots of reps." But unlike your doctor, we actually train Masters for a living, and we find that this approach works well and actually gets people stronger while not beating them up with soreness and fatigue.
Give the article a read and let me know what you think!